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We present a novel method for generating optical vortex needle beams (focused optical vortices with extended depth-of-focus) using a compact flat multilevel diffractive lens (MDL). Our experiments demonstrate that the MDL can produce focused optical vortices (FOVs) with topological charges l = 1 − 4 (extendable to other l values), maintaining focus over distances significantly longer than conventional optical vortices. Specifically, FOVs exhibit non-diffracting behavior with a depth-of-focus (DOF) extended beyond 5 cm, compared to conventional optical vortices, which show continuous size increase due to diffraction. When the MDL is illuminated by an optical vortex of 3 mm diameter, it achieves a transmission efficiency of approximately 90 % and extends the DOF several times beyond that of traditional lenses. Increasing the size of the input optical vortex further extends the DOF but introduces additional rings, with their number increasing proportionally to the value of l. Our approach, validated by both experimental results and numerical simulations, proves effective for beams such as optical vortex and Hermite-Gaussian modes and holds potential applications in high-resolution imaging, material processing, optical coherence tomography, and three-dimensional optical tweezers, offering a simple and efficient solution for generating non-diffracting beams. [ABSTRACT FROM AUTHOR]

In terahertz (THz) wireless communication systems, non-diffraction vortex beams carrying an orbital angular momentum (OAM) have attracted extensive attention due to their ability to transmit information over long distances with high capacity. However, existing metasurfaces can only generate a single OAM mode non-diffracting vortex beam at reflection space for circular polarization (CP) incidence, limiting practical applications. To address this issue, we propose and design a polarization-frequency multiplexing transmissive THz metasurface to realize multi-mode non-diffracting vortex beams at linear polarization (LP) incidence. The meta-atom of this metasurface is composed of three anisotropic rectangular metallic structures embedded in vanadium dioxide (VO2) square rings, two circular aperture metallic grid layers, and four dielectric layers. By reasonably designing the size of the metal patch and the state of VO2, the designed metasurface can achieve polarization multiplexing and frequency multiplexing for LP incidence. Based on the phase response of the proposed meta-atoms, the transmissive metasurface can implement not only multi-mode non-diffraction vortex beams but also their space separation at two frequency ranges of 0.80–0.90 THz and 1.50–1.80 THz by changing the state of VO2. Therefore, the proposed multiple multiplexing metasurfaces can effectively shape the wavefront of non-diffraction vortex beams, which have broad application prospects in 6G THz communication. [ABSTRACT FROM AUTHOR]

As an innovative neural modulation technique, the transcranial magneto-acousto-electric (MAE) stimulation (TMAES) realizes the synergistic regulation of neuronal discharge through the ultrasonic mechanical and inductive electric effects, offering significant prospects in biomedical applications. However, the stimulation accuracy is still limited by the unidirectional distribution of MAE field intensity. A method of constructing center-converging MAE field by coupling the helical wave fronts of focused acoustic-vortex (FAV) beams with a coaxial magnetic field is proposed. By describing FAVs with Laguerre–Gaussian functions, the theory of MAE field construction is derived in explicit formulae and the spatiotemporal characteristics of MAE fields in the focal region are analyzed. It is theoretically and experimentally demonstrated that the MAE field generated by the FAV of lth order is determined by those of (l − 1)th and (l + 1)th orders. The center-converging phase-rotating MAE field can only be generated by the FAV of first order, maintaining a constant peak intensity at the vortex center. Experimental distributions of MAE fields for FAVs of different orders show good agreements with numerical simulations. With the peak pressure of 0.86 MPa and the magnetic intensity of 0.3 T, the peak intensity of 62.1 mV/m reaching the electric stimulation threshold is achieved. The center-converging MAE field constructed by FAV may develop a new synergistic neural modulation scheme for TMAES with enhanced precision and flexibility while ensuring safety and efficacy, thereby exhibiting significant scientific and practical implications. [ABSTRACT FROM AUTHOR]

The analytical expressions for the cross-spectral density matrix elements of the partially coherent elegant Laguerre–Gaussian (eLG) vortex beam propagating through anisotropic turbulent plasma were derived based on the extended Huygens-Fresnel principle and used to study the changes in the polarization degree and the coherence degree of the partially coherent eLG vortex beam in the turbulent plasma. The numerical results show that the polarization degree of a partially coherent eLG vortex beam reaches a specific value (which is equal to the degree of polarization in the source plane) after a long propagation distance in the turbulent plasma. Moreover, this value is independent of the beam order, topological charge, correlation coefficient, wavelength of the source plane, anisotropy parameter, refractive index fluctuation variance, and outer and inner scales of the turbulent plasma. The results also show that with increasing distance, the coherence degree first decreases from unity and then oscillates around zero. However, this oscillation gradually disappears after traveling a long distance. Our results intuitively present the beam polarization and coherence properties through anisotropic hypersonic turbulence, which can be useful for optical communication in hypersonic turbulent environments. [ABSTRACT FROM AUTHOR]

Partially coherent perfect vortex beams with periodic coherence properties, namely, optical coherence perfect vortex lattices (OCPVLs), are proposed in this letter. Rhombus-, spiral-, and circle-shaped OCPVLs were investigated in detail both theoretically and experimentally through the manipulation of the coherent structures. Manipulating the coherence width yielded unique advantages, such as maintaining uniformity over a longer distance, more efficient optical trapping, and high-capacity free-space optical communications. OCPVLs with such advantages hold outstanding potential for applications in multi-particle trapping and manipulation. [ABSTRACT FROM AUTHOR]

The generation of multicolor (523, 605, 637, and 719 nm) optical quasiparticles (bimerons and skyrmions with topologically protected polarization textures) from a diode‐pumped Pr3+‐doped fluoro‐aluminate glass (Pr3+: WPFG) fiber simply with intra‐cavity plano‐convex lens and wedge‐plate and without any wavefront control elements, such as a spatial light modulator is demonstrated. This robust and cost‐saving system efficiently produces Bloch‐, Néel‐, and anti‐quasiparticles with high mode purity. In particular, the green optical quasiparticles will have the potential to explore many applications in materials science and biotechnologies. [ABSTRACT FROM AUTHOR]

Liquid crystal (LC) planar optics have advanced wavefront engineering toward ultrathin designs, capturing widespread attention. However, most wavefront control in LC planar optics remains constrained to freespace due to limitations in the precision of freely controllable units. Here, LC on‐chip wavefront engineering is proposed and confirmed. By controlling the initial azimuth angle of the polarization grating, the initial phase can be engineered, as theoretically predicted by rigorous coupled‐wave analysis. Experimentally, the initial azimuth angle of a polarization volume hologram grating, used as a waveguide coupler, is ingeniously modulated using a holographic template. Consequently, several on‐chip optical elements, including lenses, vortex beam generators, and holograms, are demonstrated. Furthermore, exit pupil expansion and multiexposure technologies are adopted to enhance off‐chip functionality and enable multifunctional, highly integrated LC on‐chip photonic systems. The proposed LC on‐chip wavefront engineering may find applications in freeform optics, near‐eye displays, LIDAR, and integrated photonic systems. [ABSTRACT FROM AUTHOR]

In this work, we design and implement a new bifocal diffractive spiral lens within an optical tweezers system. The proposed diffractive optical element coined Kolokaski Kinoform Spiral Lens (KKSL), generates twin optical vortices along the propagation direction. The axial positions, as well as the diameters of the generated vortex beams, are correlated with the Kolakoski aperiodic sequence introduced in the design of the diffractive lens. The unique properties of KKSLs make it ideal for optical trapping applications, allowing independent multiple trapping and particle displacement within each optical vortex beam. We present both the focusing properties of KKSL and the experimental results of its integration into the optical tweezer setup. [ABSTRACT FROM AUTHOR]

Pulsed polarized vortex beams, a special form of structured light, are generated by tailoring the light beam spatiotemporally and witness the growing application demands in nonlinear optics such as ultrafast laser processing and surface plasma excitation. However, existing techniques for generating polarized vortex beams suffer from either low compactness due to the use of bulky components or limited controlment of pulse performance. Here, an all-fiber technique combining plasmonic metafibers with mode conversion method is harnessed to generate high-performance pulsed polarized vortex beams. Plasmonic metafibers are utilized as saturable absorbers to produce Q-switched pulses with micro-second duration, while the offset splicing method is employed to partially convert the fundamental transverse mode (LP 01 ) to higher-order mode (LP 11 ). Eventually, a polarized vortex beams laser is achieved at the telecom band with a repetition frequency of 116.0 kHz. The impact of geometrical parameters including period of metafibers and offset of splicing on the spatiotemporal properties of pulsed polarized vortex beams is systematically investigated. Our findings could pave the way for design, control and generation of all-fiber pulsed polarized vortex beams, and also offer insights into the development of other types of structured laser sources. [ABSTRACT FROM AUTHOR]

Vectorial structured beam, which possesses diverse inhomogeneous spatial field distributions, has been developed into an advanced technology for particle trapping, optical communication, and quantum information. However, most of the related studies are based on static devices that can only generate structured light with fixed field distributions. To break through this restriction, the study proposes and experimentally demonstrates a reflection‐type spin‐independent programmable metasurface (SIPM) that can generate arbitrary vector vortex beams (VVBs) dynamically in microwave frequencies. By controlling the working states of loaded positive‐intrinsic‐negative (PIN) diodes, the metasurface can realize real‐time and spin‐independent manipulations of amplitude and phase of the reflected waves. Therefore, any desired VVBs can be achieved by dynamically controlling the superimposition of left‐ and right‐handed reflected circularly polarized vortexes. The proposed SIPM exhibits powerful abilities in modulating the vectorial structured beams in the microwave band, and may bring potential technological innovations for the future spintronics, imaging display, optical computing, and wireless communications. [ABSTRACT FROM AUTHOR]

Optical computing has been proven to have the ability to process information with ultra‐high speed. Here, an all‐optical feature extraction system via sparse representation (AFE‐SR) is introduced. The AFE‐SR, which is achieved by multiple diffractive optical elements (DOEs), can realize the recognition of generated physical fields with the speed of light. The sparse representation simplifies the target and improves the recognition accuracy. With the mathematical analysis principle of sparse optical features extraction and optical integration, the identification accuracy of the generation of physical fields is 100% in 2100 frames of the experimental videos. The application field of optical computing systems is extended to state recognition. [ABSTRACT FROM AUTHOR]

High‐dimensional frequency converter provides an enticing promise for establishing frequency interfaces to connect various physical systems toward the next generation of high‐capacity optical communication. The constant pursuit of high fidelity accompanied by multi‐dimensional information coding is restricted by the inherent fundamental nature of the degrees of freedom. Here, a high‐dimensional frequency converter is theoretically proposed and experimentally demonstrated, which builds a high‐fidelity interface between near‐infrared and blue‐violet wavelength. The perfect Poincaré beam exploiting the mutual orthogonality and transverse structure‐invariance of perfect vortex beam, accesses high‐dimensional spaces from spatial amplitude, phase, and polarization, and realizes the fidelity above 99% for arbitrary Poincaré states. Additionally, the trans‐spectral multiplexing utilizing the radial degree of freedom endows a superior capability in further increasing the system capacity. This proof‐of‐principle demonstration represents a key step toward the lossless transmission between different frequency domains, and has great prospects for constructing high‐capacity optical communication networks. [ABSTRACT FROM AUTHOR]

Janus metasurfaces, offering versatile light manipulation contingent on incident direction, are explored across microwave to mid‐infrared spectra. Nonetheless, prior designs often resort to spatial multiplexing or vertical stacking, entailing complex fabrication. Metallic Janus metasurfaces, owing to material properties, suffer notable Ohmic losses in the visible spectrum. In this study, Single‐layer TiO2‐based Janus metasurfaces with arbitrary polarization control is experimentally demonstrated, exhibiting directionally asymmetric functionalities in spin and orbital angular momentum (OAM). A novel Jones matrix formulation tailored for Janus metasurfaces is presented, enabling efficient generation of two asymmetric, high‐purity OAM states of vortex beams at wavelength of 532 nm, contingent on incidence direction. This innovation facilitates compact and versatile phase manipulation, encompassing applications such as lasers and optical combiners, thereby expanding its utility across diverse domains. [ABSTRACT FROM AUTHOR]

Beam shaping and polarization manipulation are of great importance for the design of microcavity lasers. Recently, topological photonic cavities have emerged as excellent platforms for surface-emitting lasers. In this class of lasers, beam engineering has not thus far been extensively studied. Here, we demonstrate how to achieve an intrinsic lateral shift of the beam emitted by a topological laser. This is achieved by designing a Kekulé-modulated topological bulk cavity, in which the continuous Kekulé modulation partially lifts a set of fourfold-degenerate Dirac cones into two twofold degeneracies. The resulting photonic cavity supports a range of interesting beam emission profiles, including vector beams with polarization winding, and laterally-shifted linearly-polarized Gaussian beams. It is possible to achieve lateral beam shifts in opposite directions and orthogonal polarizations for the degenerate photonic p-/d-orbitals, a feature that may be useful for photonic sensing applications. Topological phenomena in photonics have been found of great importance in realizing advanced semiconductor laser. Here the authors demonstrate the manipulation of the light emission profiles from a Kekulé-modulated topological bulk cavity in a topological-protection manner, where the achieved lateral beam shifts in light polarizations could be useful for the laser design and photonic sensing applications. [ABSTRACT FROM AUTHOR]

A type of vector beam arrays, called partially coherent full Poincaré (PCFP) beam arrays, is introduced and experimentally synthesized using modal-vector-decomposition method. Our experimental system involves a digital micro-mirror device, which can generate such beam arrays with controllable spatial coherence and array structure in almost real-time, enabling to test the impact of atmospheric turbulence on them. Furthermore, we experimentally examine the scintillations of four Stokes parameters (denoted as S 0 , S 1 , S 2 , and S 3 ) of PCFP beam arrays propagating through lab-simulated turbulence. The results indicate that the Stokes scintillations decrease as the number of beamlets increase or spatial coherence decreases. In contrast to S 0 scintillation (intensity scintillation), S 1 , S 2 , or S 3 scintillation is less affected by the turbulence under the same conditions. Our experimental results show that S 2 and S 3 scintillations could reduce by 67.2% and 52.4% compared to the intensity scintillation in strong turbulence. Our findings have potential applications in free-space optical communication when the Stokes parameter S 2 or S 3 is served as an information carrier. [ABSTRACT FROM AUTHOR]

Ultrafast vortex beams have significant scientific and practical value because of their unique phase properties in both the longitudinal and transverse modes, enabling multi‐dimensional quantum control of light fields. Directly generating watt‐level ultrafast vortex beams with large angular momentum has remained a major challenge due to the limitations of mode‐locked materials and existing spatiotemporal mode‐locking generation methods. In this study, quasi‐2D PEA2(CsPbBr3)n‐1PbBr4 perovskite films are prepared by an anti‐solvent method and employed for the first time in a mode‐locked resonator operating in free space. Utilizing the angle‐based non‐collinear pumping and frequency doubling techniques, the second‐order ultrafast green vortex beams with a power of up to 1.05 W and a duration of 373 ps are generated. Experimental findings demonstrate the strong nonlinear saturable absorption properties of quasi‐2D PEA2(CsPbBr3)n‐1PbBr4 perovskite films at high power levels, highlighting their considerable potential in ultrafast laser technology and nonlinear optics. [ABSTRACT FROM AUTHOR]

Vector beams have attracted widespread attention because of their unique optical properties; in particular, their combination with tight focusing can produce many interesting phenomena. The rise of 3D printing technology provides more possibilities for exploration. In this work, a cascading method involving a metamaterial and a metalens is used to generate a tightly focused field of vector beams in the terahertz band, which is prepared via 3D printing. As a proof-of-concept demonstration, a series of metamaterial modules capable of generating states of different orbital angular momentum are proposed by cascading with a metalens. The experimental results are in good agreement with the simulation results, fully verifying the feasibility of the scheme. The proposed design and fabrication strategy provides a new idea for the tight focusing of terahertz vector beams. [ABSTRACT FROM AUTHOR]

The propagation properties of a partially coherent vortex Hermite-cosine-hyperbolic-Gaussian beam (PCvHChGB) is investigated in atmospheric turbulence. The theoretical model for a PCvHChGB propagating in the turbulent atmosphere is established based on the extended Huygens–Fresnel diffraction integral and Rytov method, and the beam expression is obtained. The effects of the turbulence strength and initial beam parameters on the dynamic evolution of the PCvHChGB are analyzed numerically with comparison to the free space propagation. It is demonstrated that when the turbulence strength is higher or the input beam parameters, such as the beam order, the vortex charge, the spatial coherence length σ0, and the Gaussian waist width, are smaller, the central peak intensity rises more quickly. The intensity pattern change is faster as the wavelength is larger with a small decentered parameter b, inversely, when b is bigger, the opposite phenomenon happens. The obtained results could be beneficial to the PCvHChGB applications in optical communications and remote sensing systems. [ABSTRACT FROM AUTHOR]

This study is devoted to analyze the scattering from spherical homogeneous rain droplet particles illuminated by structured light beam i.e., Gaussian vortex beam (GVB) with different orbital angular momentum (OAM). The promising applications of intricate optical beam fields regarding environmental monitoring and detection have mesmerized the consideration of optical community. The optical effects i.e., absorption and scattering of the atmospheric environment cause intensity distribution of GVB which lowers quality of beam signal. GVB carries OAM and when it propagates in the atmosphere then its interaction with the environment constituents (rain, fog, snow, clouds, water vapours, atmospheric gases, and other particles) makes the problem quite interesting. Rainy medium is considered as a uniformly spherical shaped sphere. So, the interaction between a linearly polarized GVB and a rainy atmosphere is investigated using the generalized Lorenz–Mie theory (GLMT). The expressions for electromagnetic fields (incident + scattered + inside) of GVB are expanded using spherical vector wave functions (SVWFs). By implementing continuous boundary conditions (BCs) at the spherical surface of rain droplets, the scattering coefficients in context of beam shape coefficients are obtained. The efficiencies (scattering, extinction, and absorption), forward scattering, backward scattering, GVB attenuation as well as transmittance are computed and discussed. In addition to that, the influence of OAM mode number, beam waist radius, and incident beam operating wavelengths of rainy medium on the efficiencies, electromagnetic scattering, attenuation, and transmittance is analyzed. This study establishes the groundwork for examining the tuning capability of GVBs for rainy atmosphere at various parameters. [ABSTRACT FROM AUTHOR]

Vortex‐vector beam generators can effectively improve the channel capacity and communication accuracy, but they face the problems of narrow operating frequency band, low efficiency, and fixed function. Here, a terahertz liquid crystal cascaded metadevice is demonstrated, including a liquid crystal layer, an asymmetric metasurface layer, and a helical phase metasurface layer. The combination of liquid crystal's anisotropy and structural anisotropy from the asymmetric metasurface realizes the dynamic chirality construction. Then, the tunable chiral fields are effectively coupled with the helical geometric phase of the last metasurface layer to realize an active control between symmetric and asymmetric spin‐orbit angular momentum coupling, leading to the two types of beam generation and conversion: 1) spin‐dependent conversion and energy distribution between the vortex beams with ±2 topological charges; 2) the conversions between the 2‐order vortex beam and the cylindrical vector beam. The experimental results show that the excitation efficiency of vortex beams can reach over 92.1%, and the intensity modulation depth between different types of beams is more than 72.4%. This THz beam dynamic conversion mechanism and device scheme increase the degree of freedom of the device and have potential applications in terahertz multi‐channel wireless communication, polarization multiplexing imaging, and chiral spectrum detection. [ABSTRACT FROM AUTHOR]

Perfect vector vortex beams play a very important role in understanding complex structured beams due to their vortex nature and nonuniform polarization profiles. However, the generation of these beams suffers from a limited number of topological charges, bulky optical setup, lack of color information, and limited control along the light propagation direction. To tackle these fundamental and technical challenges, a metasurface approach to generating multiple grafted perfect vector vortex beams (GPVVBs) along the light propagation direction. GPVVBs with different colors are observed by changing the observation plane is proposed. Their polarization profiles are indirectly confirmed through the unique features in the modulated intensity profiles with an analyzer. Furthermore, the dynamic control of these beams is realized by continuously changing the incident polarization. Simultaneous control of color and topological charges in GPVVBs along the longitudinal direction provides more degrees of freedom for carrying information and has the potential to impact quantum science, singular optics, and optical communications. [ABSTRACT FROM AUTHOR]

In recent years, the emergence of metasurfaces has brought revolutionary changes to the generation and processing of vortex beams, triggering widespread research interest. Meanwhile, the longitudinally varying features of propagating beams provide new design freedom for realizing multi‐dimensional optical manipulation and promote the advancements of related areas such as microscopic detection, microfabrication, and biomedical applications. In addition, self‐accelerating Bessel beams are promising for a wide range of applications such as particle manipulation and medicine due to their nondiffracting, self‐healing as well as obstacle avoidance properties. In this paper, a novel kind of curved transmitted high‐order Bessel beams with longitudinally varying features based on form‐birefringent metasurface, by simultaneously manipulating the phase profiles of output orthogonal polarization components is demonstrated. Multiple dimensions of the beam, including the propagation trajectory, polarization state, and orbital angular momentum, can be tailored arbitrarily. For verifying the feasibility of the demonstrated method, two samples with different propagation trajectories, as well as different variations of orbital angular momentum, are designed and experimentally demonstrated. Such a novel approach can open new doors for the manipulation of vortex beams and can be used for depth sensing and distance measurement in complex environments. [ABSTRACT FROM AUTHOR]

This work report the generation of high‐order Laguerre–Gaussian (LG) modes from a nanosecond, optical vortex pumped diamond Raman laser. This system is capable of generating first‐Stokes (λ1st = 1240 nm) LG modes with topological charge (ℓ) of up to 26 and second‐Stokes (λ2nd = 1485 nm) LG modes with topological charge of up to 22, when pumped using a first‐order vortex beam. The maximum first‐ and second‐Stokes LG mode energies are measured to be 0.5 and 1 mJ, respectively, when pumping with energy of 19.8 mJ. [ABSTRACT FROM AUTHOR]

Arrays of multiple vortex beams enhance parallel processing capabilities from particle manipulation to information communication. However, the spatial position, topological charge, and energy parameters of the vortex beams within the array have yet to be precisely controlled, posing significant challenges to the realization of multi‐view 3D Orbital Angular Momentum (OAM) display using vortex arrays as information carriers. To address this issue, a method for generating vortex arrays based on a phase‐only hologram, customizing the array by using the energy and OAM spectrum of each vortex beam as the loss function is developed. Experimental results indicate that a 2D array generates 100 vortex beams in the spatial frequency domain, while a 3D array in the Fresnel zone produces 252 vortex beams across 7 planes, each with 36 unprecedentedly controllable energy and topological charge vortex beams. Subsequently, images of 4 views using the 3D vortex arrays and decoded through coordinate transformation to achieve a multi‐view 3D OAM display are encoded. The results demonstrate imaging quality with Mean Peak Signal‐to‐Noise Ratio (MPSNR) of 12.7, 13.0, 13.4, and 12.2 dB in 4 views, respectively, offering promising opportunities for applications in 3D optical manipulation, high‐capacity communication, and 3D OAM holography. [ABSTRACT FROM AUTHOR]

Although orbital angular momentum (OAM) is extensively explored and researched in various scientific domains, its practical application in wireless communications still faces numerous challenges. Notably, existing OAM beam generation technologies need to meet the diversified demands of modern wireless communication, such as miniaturization, cost‐effectiveness, and system integration. Driven by the immense potential of OAM in communication systems, in this work, an innovative method based on leaky cables capable of simultaneously generating multiple vortex beams, overcoming a series of implementation issues associated with multiplexing emitters, is introduced. A design prototype is fabricated and tested, and the measurement results align closely with the simulations, validating the multifunctionality and practicality of the method. Moreover, the proposed strategy can seamlessly extend to optical frequencies using the concept of leaky fibers. In this method, not only efficient spatial utilization and excellent isolation are realized but also high cost‐effectiveness is possessed. Compared to previous strategies, this technique may have an impact on simplifying the establishment of communication system platforms based on OAM multiplexing. [ABSTRACT FROM AUTHOR]

We study the formation of surface relief structures in azo-polymers generated via two-photon induced photoisomerization using a femtosecond near-infrared optical vortex laser beam. These structures exhibit exotic flower-like shapes with petals along the azimuthal direction, and they are formed from spatial mode instability, which is associated with third-order nonlinear effects in the azo-polymer. This process is a unique and exotic interaction between light and matter, which may be applied to the development of advanced optical data storage technologies. Here, an additional degree of freedom is offered by the number of formed petals, which themselves are a function of the topological charge of the optical vortex beam. [ABSTRACT FROM AUTHOR]

Transverse mode control of laser intracavity oscillation is crucial for generating high-purity cylindrical vector beams (CVBs). We utilized the mode conversion and mode selection properties of two-mode long-period fiber gratings (TM-LPFGs) and two-mode fiber Bragg gratings (TM-FBGs) to achieve intracavity hybrid-mode oscillations of LP01 and LP11 from an all-few-mode fiber laser. A mode-locked pulse output with a repetition rate of 12.46 MHz and a signal-to-noise ratio of 53 dB was achieved with a semiconductor saturable absorber mirror (SESAM) for mode-locking, at a wavelength of 1550.32 nm. The 30 dB spectrum bandwidth of the mode-locked pulse was 0.13 nm. Furthermore, a high-purity CVB containing radially polarized and azimuthally polarized LP11 modes was generated. The purity of the obtained CVB was greater than 99%. The high-purity CVB pulses have great potential for applications in optical tweezers, high-speed mode-division multiplexing communication, and more. [ABSTRACT FROM AUTHOR]

This paper presents a novel method for generating and shaping reverse energy flow through the interference of light fields from a minimal number of point light sources. Until now, reverse energy flow has only been observed using complex light fields, such as optical vortices or cylindrical vector beams, limiting the formation of reverse energy flow near the optical axis. We demonstrate both analytically and numerically that unbounded regions of reverse energy flow can be achieved with just two point light sources, positioned asymmetrically at specific angles (e.g., 90 or 45 degrees) and with particular polarization states. The results indicate that the relative reverse energy flow can be enhanced by increasing the number of sources to three or four, adjusting their polarization, or introducing a vortex phase singularity. The presence of an initially embedded asymmetry in the fields under consideration leads to the formation of a non-uniform distribution of spin and orbital angular momentum density. Variations in the polarization state, as well as the introduction of a vortex phase singularity, allow for changing the distribution of angular momentum density while maintaining the presence of a reverse energy flow. We also explore the feasibility of implementing the obtained results using sectional phase diffractive optical elements, which will enhance the energy efficiency of the generated fields compared to point sources. [ABSTRACT FROM AUTHOR]

(1) Background: The significant progress observed over the last two decades in coherent beam combining (CBC) technology has mainly focused on its applications in high-energy physics and laser weapons. This work provides insight into the basic principles of CBC and the search for an alternative, namely optical angular momentum (OAM) generation using CBC. (2) Methods: A semi-analytical model based on the paraxial wave equation was explored, generating OAM-CBC beams by manipulating the tilts and phases of the CBC (T&P-CBC) of hexagonal architecture. (3) Results: The specially arranged T&P-CBC shows typical properties of OAM, such as annular profiles for the zero diffraction order and 1st-order replicas in the far field and correlation coefficients of 1% between different OAM-CBC fields. (4) Conclusions: The differences between classical OAM beams and OAM-CBC are substantial due to hexagonal lattice properties. Moreover, applications in free space optical communications are feasible as T&P CBC fulfills the main conditions and requirements for OAM generation. [ABSTRACT FROM AUTHOR]

The field of high-bandwidth holography has been extensively studied over the past decade. Orbital angular momentum (OAM) holography, which utilizes vortex beams with theoretically unbounded OAM modes as information carriers, showcases the large capacitance of hologram storage. However, OAM holography has been limited to a single wavelength, restricting its potential for full-color holography and displays. In this study, we propose wavelength and OAM multiplexed holography that utilizes the multiple dimensions of light—wavelength and OAM—to provide a multi-color platform that expands the information capacity of holographic storage devices. The proposed wavelength-OAM multiplexed holography is physically realized by a metasurface, the state-of-the-art optical element consisting of an array of artificially engineered nanostructures. Hydrogenated silicon meta-atoms, the constituents of the metasurface, are engineered to possess wavelength selectivity by tailoring the dispersion of polarization conversion. These meta-atoms are used to encode the calculated OAM-preserved phase maps based on our design. The sampling grid of the phase map is rotated by 45°, which effectively suppress higher-order diffraction, providing a great strategy for achieving large field-of-view (FOV) holography. We successfully demonstrate six holographic images that are selectively reconstructed under the illumination of light with specific wavelengths (λ = 450, 635 nm) and topological charges (l = -2, 0, 2), without high-order diffraction. Our work suggests that ultrathin meta-holograms can potentially realize ultrahigh-bandwidth full-color holography and holographic video displays with large FOV. [ABSTRACT FROM AUTHOR]

Programmable metasurfaces show enormous potential in real-time electromagnetic (EM) manipulation and their stable responses to variable EM waves including incident angle and polarization changes are crucial for related applications. However, the demonstrated programmable metasurfaces are commonly considered in normal-incident waves with fixed polarization; how to achieve stable performance in more realistic scenarios of wide-angle and full-polarized wave incidences is still a challenge. Here, we propose and realize a wide-angle and full-polarization programmable metasurface, which can generate stabilized amplitude and phase responses at both transverse electric (TE) and transverse magnetic (TM) oblique incidences. These are achieved by introducing metallic walls around the metasurface element to reduce element coupling, which greatly improves the angular stability of its reflection responses. The mechanisms of angular insensitivity are analyzed comprehensively, and as a proof of concept, obliquely-incident beam steering, large-angle beam scanning and oblique vortex beam emitting are demonstrated on this programmable metasurface. Both the simulation and experimental results demonstrate that the programmable metasurface can operate well at both TE and TM wide-angle oblique incidences in the upper half space. Our work offers an actual route for improving the angular stability and polarization insensitivity of metasurfaces, which could push them one step closer towards more complicated applications. [ABSTRACT FROM AUTHOR]

Vector light beams, characterized by a spatially varying polarization, can exhibit localized structures reminiscent of the skyrmions familiar from the study of magnetic media. We present a theory of such skyrmions within paraxial optics, exploiting mathematical analogies with the study of superfluids, especially the A phase of superfluid He3. The key feature is the skyrmion field, which, together with the underlying skyrmion vector potential, determines the properties of the skyrmions and, more generally, the polarization structure of every paraxial vector beam. In addition to structures with integer skyrmion numbers, we find polarization patterns with non-integer skyrmion numbers; these seem to have no analogue in other fields of physics. [ABSTRACT FROM AUTHOR]

We proposed a method to measure the topological charge of a vortex beam by using the self-rotating beam phase in this Letter. We investigated the far-field intensity patterns of the vortex beams passing through a phase hologram of the self-rotating beam with n = +2 theoretically and experimentally. The results demonstrate that the far-field intensity patterns cannot exhibit bright stripes when the topological charge of the vortex is positive (i.e., n ⋅ l > 0) and the calculated ratio relationship ξ can be used to identify the topological charge of the vortex beam. Differently, it can be found that the far-field intensity patterns exhibit several bright stripes when the topological charge of the vortex is negative (i.e., n ⋅ l < 0) and the number N of the bright stripes is equal to |l|−1(l represents the topological charge of the vortex beam). The experimental results are in good agreement with the theoretical ones. This method may inspire further research in the field of self-rotating beams. [ABSTRACT FROM AUTHOR]

The integration of multiple functionalities into a single, planar, ultra-compact metasurface has presented significant opportunities for enhancing capacity and performance within compact 5G/6G communication systems. Recent advances in multifunctional metasurfaces have unveiled comprehensive wavefront manipulations utilizing phase, polarization transmission/reflection, and coding apertures. Despite these developments, there remains a critical need for multifunctional metasurfaces with expanded channel capabilities, including multiple operational frequencies, minimal crosstalk, and high-efficiency computable array factors. This study introduces a multifunctional metasurface that integrates phase- and amplitude simultaneous coding meta-atoms at dual frequencies. By altering the polarization of electromagnetic (EM) waves, it is possible to reshape the wave-fronts of reflected waves at these frequencies. The coding metasurface proficiently manipulates both x and y linearly polarized waves through phase and amplitude coding at dual frequencies, thereby enabling distinct functionalities such as anomalous reflection, reflection imaging, and vortex wave beam generation. Both theoretical analysis and full-wave simulation confirm the anticipated functionalities of the designed devices, paving the way for advancements in integrated communication systems with diverse functionalities. [ABSTRACT FROM AUTHOR]

In this study, the nonlinear optical phenomena emerging from the interaction between vortex and vector beams and achiral nanoparticles or nanostructures are investigated. Despite the achiral symmetry of the nanostructure, the interplay between the symmetries of the vortex beam, the nanostructure, and the crystalline lattice of the nanostructure material can result in circular dichroism in the nonlinear regime. A formula is derived that describes the conditions for the appearance of circular dichroism across a broad range of scenarios, taking into account all the symmetries. Building on these findings, the conditions for both linear and nonlinear dichroism when illuminated by vector beams have been determined. This work can provide important insights that can enhance the design of chiral sensors and optical traps, making them more versatile and effective. [ABSTRACT FROM AUTHOR]

Photonic integrated circuits (PICs) are iterating on electronic ones to enable higher‐speed parallel computing while meeting the growing demands for energy efficiency in big‐data processing. However, manufacturing multi‐layered and 3D PICs remains challenging based on conventional planar lithography. Here, a rapid prototyping technique is delineated to configure large‐area and 3D PIC in glass based on laser‐direct written optical waveguides by employing femtosecond cylindrically polarized vortex laser beams. The vortex laser beam is mathematically rotationally invariant and capable of conformally transforming waveguide cross‐sections at arbitrary bending angles of 0–90° and across a large depth change. Based on this approach, a one‐layer 12‐core waveguide circuit with a variable cross‐section (diameter 5–11.5 µm) while maintaining a high mode ellipticity >0.974, as well as a more complex three‐layer 36‐core connector in which the waveguide dives continuously from 50 µm to 550 µm with a small loss difference of <0.1 dB is demonstrated. This work offers a pathway for 3D imprinting of large‐area photonic circuits in glass and other transparent materials, which has potential applications in high‐efficiency photonic computing, multidimensional quantum networks, and 3D optics topology. [ABSTRACT FROM AUTHOR]

The scattering phenomena can be realized in a variety of everyday situations, including the rainbow pattern after a rainstorm, the dispersion of raindrops, information and communication (ICT) systems, radar cross section (RCS) measurement, and remote sensing. Inspired by the electromagnetic scattering features, this study explores the scattering characteristics of orbital angular momentum (OAM) carried by Gaussian vortex beam (GVB) for perfect electromagnetic conductor (PEMC) sphere by utilizing the generalized Lorenz–Mie theory (GLMT). Stemming from the integral localized approximation (ILA) method, the beam‐shape coefficients (BSCs) representing the incident GVB are obtained. Vortex beams carry distinct unique optical characteristics as compared to the other beam types as these possess OAM. Computations for the efficiencies (scattering and extinction) for a focused GVB are conducted and discussed to analyze the scattering phenomena of the electromagnetic fields outside the PEMC sphere. To ensure the accuracy of the results, scattering efficiency for Gaussian beam and plane wave is computed and compared using the GLMT for PEMC sphere. The OAM mode index, beam waist radius, and the scalar admittance of GVB are chosen as parameters to investigate their impact on the scattering dynamics (i.e., scattering and extinction efficiency). The numerical results show that OAM mode index, beam waist radius, and PEMC admittance have greater impact on optical efficiencies. Nonetheless, the trend of the scattering efficiency decreases irrespective of the extinction efficiency i.e., increases for OAM mode index. [ABSTRACT FROM AUTHOR]

Light contains both spin and orbital angular momentum. Despite contributing equally to the total photonic angular momentum, these components derive from quite different parts of the electromagnetic field profile, namely its polarization and spatial variation, respectively, and therefore do not always share equal influence in light–matter interactions. With the growing interest in utilizing light's orbital angular momentum to practice added control in the study of atomic systems, it becomes increasingly important for students and researchers to understand the subtlety involved in these interactions. In this article, we present a review of the fundamental concepts and recent experiments related to the interaction of beams containing orbital angular momentum with atoms. An emphasis is placed on understanding light's angular momentum from the perspective of both classical waves and individual photons. We then review the application of these beams in recent experiments, namely single- and few-photon transitions, strong-field ionization, and high-harmonic generation, highlighting the role of light's orbital angular momentum and the atom's location within the beam profile within each case. [ABSTRACT FROM AUTHOR]

In this work, we demonstrate a Watt-level, high-quality Laguerre–Gaussian (LG) LG0±1 vortex mode directly output from an end-pumped Nd:YVO4 laser by using an axicon-based annular pump beam. A theoretical model for the annular beam end-pumped solid-state laser with an LG vortex mode output was established. Chirality control of the vortex laser was achieved by carefully tilting the output coupler. Watt-level 1064 nm lasers with pure LG0,1/LG0,−1 vortex mode, and the incoherent superposition mode of LG0,1 odd and even petal modes, were achieved successively in our experiments. The intensity profile of the generated pure LG0,1 vortex laser was measured, and it can be well fitted by using the standard expression of the LG0,1 vortex mode. The beam quality of the pure LG0,1 mode is Mx2 = 2.01 and My2 = 2.00 along the x-axis and y-axis, respectively. Our study demonstrates that that axicon-based annular pumping has great potential in developing high-power vortex solid-state lasers with simple and compact structures. [ABSTRACT FROM AUTHOR]

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This paper investigates a new vortex wave imaging approach to improve the imaging quality of small metal targets of size less than 1.5 mm. Antennas with different spiral phase plates are designed to efficiently transmit vortex beams with orbital angular momentums (OAMs). By analyzing the OAM spectrum of the target, it was discovered that the predominant reflection contains a particular OAM mode that carries abundant azimuthal information. This can be explained by the OAM selectivity of the target and the guidance of the vortex transmitting beam. A simple reflection vortex imaging system was designed to capture the phase information. Measurement results show that the high image contrast reaches 14.9%, which is twice as high as that of the imaging without OAM. Both of simulations and experiments demonstrate that the vortex phase imaging approach proposed in this paper can effectively improve the imaging quality at 80 GHz. This approach is suitable for other millimeter wave imaging systems and is helpful to improve the resolution in anti-terrorism security checks. [ABSTRACT FROM AUTHOR]

We propose a scheme to investigate the spatial modulation of the refractive index in a dense atomic ensemble under the action of the Laguerre–Gaussian (LG) beams. Theoretical derivations based on a density-matrix approach associated with numerical simulations are utilized to study the behaviors of the index of refraction, showing that the azimuthal and radial mode indices (i.e., l 2 and p 2) of the LG beams significantly affect the real and imaginary parts of the refractive index. To be specific, the number of the dispersive peaks is determined by (p 2 + 1) | l 2 | , and there are 2 | l 2 | lossless petals in conjunction with p 2 concentric absorption rings centered on the vortex center. Furthermore, by tuning the phase values of the electric and magnetic components of the electromagnetic field, the index of refraction can be drastically tuned from negative to zero to positive and accompanied by periodic absorption and amplification. This investigation provides a powerful tool for manipulating the index of refraction through a nonlinear interaction between atoms and the vortex beams and suggests potential applications in optical switching, logic gates, and optical storage with spatially varying refractive indices. [ABSTRACT FROM AUTHOR]

Surface plasmon polaritons (SPPs) are electromagnetic waves that travel along a metal–dielectric interface and are finding an ever-increasing number of applications in newly emerging nano-photonic and optoelectronic technologies. Different from the traditional approach to excite SPPs using prism or grating, metallic metasurfaces incorporating nano-slots with different orientations enable the photonic spin-dependent directional coupling of SPPs, which shows the unique spin tunability. However, the propagations of these generated SPPs are still correlative due to the conjugated phase profiles of metasurfaces for two incident orthogonal spin states. Here, we propose a plasmonic spin-multiplexing metasurface composed of nano-slots with different geometric dimensions and orientations to efficiently control the near-field generation and in-plane propagation of SPPs. By taking into account both the geometric phase and resonant phase of the nano-slots, the metasurface can generate two independent and fully decoupled SPP fields for a pair of orthogonal spin states. As proof-of-concept, we design a series of spin-multiplexing metasurfaces to numerically demonstrate different near-field optical functionalities, including spin-controlled plasmonic bi-focusing, self-accelerating beams, and vortices. We envision this approach may have potential applications in designing polarization-dependent tunable plasmonic nano-devices. [ABSTRACT FROM AUTHOR]

For the application of vortex electromagnetic (EM) beams in practical detection scenes, the scattering characteristics of electrically large arbitrarily shaped targets illuminated by an off-axis Laguerre–Gaussian (LG) vortex beam are investigated and compared to the on-axis incidence case. The vector potential method is used to extract the electric and magnetic field components of the LG beam in different polarization states. The physical optics algorithm is adopted to calculate the scattering fields of four typical targets with the shape of a sphere, NASA almond, blunt cone, and blade model. The results revealed that as the beam center offset and the topological charge of the incident vortex beam increase, the scattering field distorts, and the obvious orbital angular momentum (OAM) spectrum mixing occurs. In addition, OAM spectrum aliasing occurs for asymmetric targets, even at on-axis incidence. These results elucidate the mechanism of vortex EM scattering and provide a reference for applying vortex beams for target detection and recognition. [ABSTRACT FROM AUTHOR]

In recent years, topological physics has attracted broad attention in condensed matter systems. Here, we report an experimental study on topological valley transport of spoof surface acoustic waves (SAWs). Specifically, we realize valley pseudospins and a valley Hall phase transition by tuning the structural size of adjacent grooves. In addition to a direct visualization of the vortex chirality-locked beam splitting for the bulk valley states, valley-projected edge states are observed in straight and bent interface channels formed by two topologically distinct valley Hall insulating phases. The experimental data agree well with our numerical predictions. The topological transport of spoof SAWs, encoded with valley information, provides more possibilities in design novel acoustic devices based on the valley-contrasting physics. [ABSTRACT FROM AUTHOR]

Overshadowed by the electric dipole ones, the magnetic dipole transitions of a quantum emitter are hard to probe. This can be remedied by using pure magnetic hotspots, which host strong magnetic but quite weak electric fields in a subwavelength region. Utilizing the multiparticle Mie theory, we demonstrate pure magnetic hotspots via hollow silicon nanoparticles arranged in a ring configuration and illuminated by Bessel cylindrical vector beams. Normalized local field admittances of about 10 5 – 10 7 and magnetic field enhancements of about 10–30 are achievable. Moreover, the peak of the magnetic field enhancement can be shifted about 370 nm via the hollow size. In other words, the pure magnetic hotspot can be optimized for a particular magnetic dipole transition. [ABSTRACT FROM AUTHOR]

Laguerre–Gaussian (LG) beams with a spiral phase (optical vortex), which feature orbital angular momenta, and vector beams (VBs) with an axially symmetric spatial polarization distribution exhibit properties different from those of conventional Gaussian beam. In this article, we introduce LG beams and VBs. Next, we explain the generation of LG beams and VBs using liquid-crystal devices. Subsequently, we report the super-resolution observation of biological samples and our observation of a PNLC (Polymer network liquid crystal) network structure using a laser scanning microscope, which comprises a liquid crystal LG-VB generator. Finally, we discuss the conservation of spiral beams and their application to optical wireless communication. [ABSTRACT FROM AUTHOR]

High-order vortex beams carrying orbital angular momentum in the visible wavelength range are of tremendous interest for a diversity of applications, including super-resolution imaging, microfabrication, and underwater communications. Such beams can be generated directly from compact solid-state lasers; however, they generally have low topological charge number. In this work, we demonstrate the generation of high-order Laguerre–Gaussian (LG) modes from a simple Pr:YLF laser cavity and demonstrate its application in the measurement of angular velocity. We utilize enhanced intracavity spherical aberration to generate LG0,±m modes with m selectable up to 34, directly from a Pr:YLF laser operating at 640 nm. We utilize this laser beam in an off-axis illumination geometry in conjunction with the rotational Doppler effect, to measure the angular velocity of a spinning object. The demonstration highlights a potential application for these types of vortex laser. [ABSTRACT FROM AUTHOR]

Material anisotropy and chirality produce polarization‐dependent light‐matter interactions. Absorption leads to linear and circular dichroism, whereas elastic forward scattering produces linear and circular birefringence. Here a form of dichroism and birefringence is highlighted whereby generic anisotropic media display locally different absorption and scattering of a focused vortex beam that depends upon the sign of the topological charge ℓ$\ell$. The light‐matter interactions described in this work manifest purely through dominant electric‐dipole coupling mechanisms and depend on the paraxial parameter to first‐order. Previous topological‐charge‐dependent light‐matter interactions require the significantly weaker higher‐order multipole moments and are proportional to the paraxial parameter to second‐order. The result represents a method of probing the nano‐optics of advanced materials and the topological properties of structured light. [ABSTRACT FROM AUTHOR]

Metasurface‐based vortex beams are expected to overcome the current communication challenges of massive data and limited bandwidth by their theoretical infinite and mutually orthogonal states. However, limited by the spatial extension of array vortices, only finite orbital angular momentum (OAM) eigenstates are available, of which the expansion will boost the bandwidth toward an inexhaustible stage. In this manuscript, multi‐concentric generalized perfect vortex beams (G‐PVBs) are experimentally generated by the fabricated hybrid phase metasurfaces integrating generalized focusing phases and circular domain function into vortex phases. Diverse vortex shapes and helical lobes within beam patterns and spiral interferograms are both arranged in a non‐overlapping concentric manner instead of spatial arrays, respectively, breaking the limitation of symmetric shape while avoiding inter‐modal cross‐talk. The vortex shape, topological charge and vortex number are decoupled mutually in orthogonal polarization states, realizing both space and polarization multiplexing. Furthermore, shaped into anomalous profiles with asymmetric states of polarization, multi‐concentric vector G‐PVBs are experimentally generated to transmit parallelly stable order information with high robustness in turbulence environments. The proposed multi‐concentric G‐PVBs simultaneously expanded the novel vortex dimension by anomalous shapes and information channels of multi‐concentric OAM modes, providing potential application in high‐capacity vortex optical communication and information encryption. [ABSTRACT FROM AUTHOR]